Light availability and soil compaction influence the growth of underplanted Nothofagus following partial shelterwood harvest and soil scarification

We evaluated effects of topsoil scarification by heavy machinery on growth of two valuable, shade-intolerant tree species--Nothofagus dombeyi (Mirb.) Oerst. (evergreen and considered to be very plastic to different soil fertility levels) and Nothofagus alpina (Poepp. & Endl.) Oerst. (deciduous and considered to be sensitive to soil fertility) - seedlings that were underplanted in Nothofagus old-growth forests, which were subjected to shelterwood cuttings without the final cut in the Chilean Andes. We compared tree basal diameter growth as it responds to light availability and soil compaction (as measured by resistance to penetration) by fitting a growth model based on the Michaelis-Menten equation. Predicted growth of N. dombeyi was greater than N. alpina in high and low light levels; however, there were no significant differences between the species. Both species showed significant differences at high levels of penetration resistance (>2000 kPa). Differences for N. dombeyi occurred above ~40% in total light, and differences occurred for N. alpina above ~20% in total light. However, they were not different when compared at low and intermediate levels of penetration resistance. The results suggest that partial shelterwood cuts may provide adequate light levels to achieve appropriate growth of underplanted Nothofagus seedlings. However, if regeneration of N. alpina is desired, scarification of topsoil needs to be implemented with more caution in canopy openings, as traffic and soil removal by heavy machinery can have detrimental effects on growth of this species and other species that are more sensitive to soil compaction. Key words: Michaelis-Menten, shade tolerance, soil resistance to penetration, stress conditions, underplanting. Nous avons evalue les effets du scarifiage de la couche superieure du sol avec de la machinerie lourde sur la croissance de semis de deux especes d'arbre precieuses et intolerantes a l'ombre, Nothofagus dombeyi (Mirb.) Oerst. (espece a feuilles persistantes qui est consideree comme etant tres plastique a differents niveaux de fertilite du sol) et Nothofagus alpina (Poepp. & Endl.) Oerst. (espece decidue qui est consideree comme etant sensible a la fertilite du sol). Ces semis ont ete plantes sous le couvert de vieilles forets de Nothofagus soumises a des coupes progressives sans la coupe finale dans les Andes chiliennes. Nous avons relie la croissance en diametre au collet des semis a la disponibilite de la lumiere et a la compaction du sol (mesuree par la resistance a la penetration) en ajustant un modele de croissance fonde sur l'equation de Michaelis-Menten. La croissance predite de N. dombeyi etait plus grande que celle de N. alpina sous des intensites lumineuses forte et faible, mais sans qu'il y ait de differences significatives entre les especes. Des differences significatives ont ete observees chez les deux especes lorsque la resistance a la penetration etait elevee (>2000 kPa). Les differences ont ete observees chez N. dombeyi au-dessus de ~40 % de la lumiere totale alors qu'elles l'ont ete au-dessus de ~20 % dans le cas de N. alpina. Toutefois, aucune difference n'a ete observee lorsque la resistance a la penetration etait faible ou intermediate. Ces resultats indiquent que les coupes progressives peuvent procurer des niveaux de lumiere adequats pour obtenir une croissance appropriee des semis de Nothofagus plantes sous couvert. Cependant, si on desire que la regeneration de N. alpina s'etablisse, le scarifiage de la couche superieure du sol doit etre realise plus prudemment dans les ouvertures du couvert parce que la circulation et l'enlevement du sol par la machinerie peuvent avoir des effets nefastes sur la croissance de cette espece et d'autres qui sont plus sensibles a la compaction du sol. [Traduit par la Redaction] Mots-cles: Michaelis-Menten, tolerance a l'ombre, resistance du sol a la penetration, conditions de stress, plantation sous couvert.
Introduction Silvicultural practices manage canopy structures with the objective of regenerating and reallocating growing space for desired crop species (Nyland 2002; Puettmann et al. 2008a). Questions on which resource levels [...]